Crop Protection Products for Organic Agriculture - ACS Publications

Chapter 17

Downloaded by CORNELL UNIV on August 6, 2012 | http://pubs.acs.org Publication Date: December 14, 2006 | doi: 10.1021/bk-2007-0947.ch017

Environmental Fate and Ecological Impact of Copper Hydroxide: Use of Management Practices to Reduce the Transport of Copper Hydroxide in Runoff from Vegetable Production 1

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Pamela J. Rice , Jennifer A. Harman-Fetcho , Lynne P. Heighton , Laura L. McConnell , Ali M. Sadeghi , and Cathleen J. Hapeman 2

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Agricultural Research Service, U.S. Department of Agriculture, St. Paul, M N 55108; Agricultural Research Service, U.S. Department of Agriculture, Beltsville, M D 20705

Vegetable production practices combining copper-based pesticides with polyethylene mulch create conditions for highly toxic runoff emissions to surface waters. Copper hydroxide is a widely used fungicide-bactericide approved for both organic and conventional agricultural production o f vegetable crops for control of diseases. Copper-based pesticides are often viewed as more "natural" than synthetic organic pesticides, but aquatic biota, such as the saltwater bivalve Mercenaria mercenaria, are extremely sensitive to low concentrations of copper. The use of polyethylene mulch in organic and traditional vegetable production is gaining popularity because it decreases pesticide use and warms the soil allowing for earlier crop planting, but its use also increases runoff volume and soil erosion. Two field studies were conducted to evaluate the effectiveness o f management practices to reduce loads of copper in runoff from tomato production. Seasonal runoff losses o f 20 to 36% of applied copper hydroxide were observed in tomato plots using plastic mulch with bare soil furrows. The addition o f vegetative furrows between the raised, polyethylene-covered beds or the replacement o f polyethylene mulch with vegetative residue

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U.S. government work. Published 2007 American Chemical Society. In Crop Protection Products for Organic Agriculture; Felsot, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2006.

231 mulch reduced copper loads in runoff by an average of 72 and 88%, respectively, while maintaining harvest yields. Use of these alternative management practices could reduce surface water concentrations in nearby streams from the observed 22 μg/L to approximately 6 and 3 μg/L, respectively, which would be below the median lethal concentration for larval clams (M. mercenaria 96-h LC =21μg/L)and close to or below the E P A guidelines to protect aquatic life (24-h average = 5.4 μg / L for fresh water and 4.0 μg /L for salt water).


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Organic agriculture is defined as an ecological production management system that promotes and enhances biodiversity, biological cycles, and soil biological activity. Certified organic cropland doubled during the five year period of 1992 to 1997, and in 1999, organic food retail sales reached six billion dollars (/). The U S D A estimated -8000 certified organic farms in 2003 were operating on 1.5 million acres of cropland and 0.75 million acres of pasture (2). Copper-based materials are allowed by U S D A National Organic Program (NOP) standards for the control of plant diseases in organic crop production provided they are used in a manner that minimizes copper accumulation in the soil (3). Copper hydroxide is a widely used fungicide-bactericide often applied prophylacticly for control of vegetable diseases. The estimated annual use of copper for fresh-market tomato production throughout the United States is 342,000 kg of active ingredient (4). Copper hydroxide (water solubility = 2.9 mg/L at pH 7,25°C) readily sorbs to soil (5-7). Polyethylene mulch (a thin sheet of black plastic) is a popular production practice for fresh-market vegetables and other row crops in traditional agriculture because it controls weeds and prevents soil from depositing on crops. Black polyethylene mulch also warms the soil and allows earlier planting. According to the N O P standards, mulches are allowed for use in organic crop production provided they are biodegradable or are synthetic mulches (i.e., polyethylene) that are to be removed after harvest (3). A 1994 survey of organic vegetable growers revealed that 21% grew fresh-market tomatoes as their main crop, and that 40 to 57% used polyethylene mulch for insect, disease, and weed control (#). Studies have shown that typically 1 to 6% of applied agrochemicals are removed from agricultural areas due to surface runoff (9). However, polyethylene mulch is impermeable and significantly reduces rainfall infiltration leading to increased runoff volumes and soil erosion (70-/2), and greater pesticide loads with runoff weeks after application (70, 75). Thus, the combined

In Crop Protection Products for Organic Agriculture; Felsot, A., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2006.

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use of polyethylene mulch with copper hydroxide would be expected to negatively impact nearby ecosystems since elevated levels of copper have been shown to affect aquatic organisms adversely (14-18). This runs countercurrent to organic agriculture's primary goal of optimizing the health and productivity of the interdependent communities of soil life, plants, animals, and people (7). The objective of this research was to compare the conventional polyethylene mulch management practice (POLY-Bare: polyethylene-covered beds with bare soil furrows) with two alternative management practices (POLY-Rye: polyethylene-covered beds with rye covered furrows; V E T C H : hairy vetch residue mulch on beds and furrows) to evaluate their effectiveness in reducing soil erosion and concomitantly decreasing copper loads in runoff.

Materials and Methods

Site Description and Management Practices The study site was located at the Henry A . Wallace Beltsville Agricultural Research Center, Beltsville, Maryland. The field, composed of Mattapex silt loam, had an average slope of 5.8% north to south and 2.6% east to west and was divided into sixteen, 162-m plots that were prepared in a north-south direction. A randomized complete block design was used to assign eight plots to tomato production while the remaining eight plots were planted with corn. Tomato and corn plots were rotated annually to reduce pest pressure. Each tomato plot contained four raised beds and earthen berms to guide runoff from the three central furrows to a fiberglass Η-flume. Runoff from the tomato plots was measured and collected using an automated flow meter and runoff sampler containing twenty-four 350-mL glass bottles (ISCO model 6700, Lincoln, N E , USA). During the 1998 and 1999 field seasons, four tomato plots were assigned to each of the following treatments: 1) tomatoes grown on raised polyethylenecovered beds with bare soil furrows between the beds (POLY-Bare) or 2) tomatoes grown on raised beds with both beds and furrows covered with hairy vetch residue mulch (VETCH). In the 2000 and 2001 field seasons, four tomato plots were assigned to each of the following treatments: 1) POLY-Bare or 2) tomatoes grown on raised polyethylene-covered beds with cereal rye planted in the furrows between the beds (POLY-Rye). Kocide® 101 (Griffin Corporation, Valdosta, G A , U S A ) , a fungicide and bactericide containing 77% copper hydroxide, was applied at recommended rates three or four times during the 2


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latter part of the growing season. Additional site characteristics and management practice details, pesticide application schedules, and precipitation events are presented elsewhere (13, 19).


Precipitation Events and Runoff Collection A tipping-bucket rain gage was used to measure the time and intensity of each precipitation event. ISCO 6700 automated runoff-samplers installed at the edge of each plot were equipped with a bubbler flow module (model 730). Each was programmed to collect samples on a flow-weighted (volume) basis. Individual and integrated water samples were characterized in terms of total suspended solids, total copper, or dissolved- and particulate-phase copper.

Copper Extraction and Analysis Runoff samples were filtered to separate the dissolved-phase (< 0.45 μιη) from the particulate-phase (> 0.45 μπι) copper. Dissolved-phase copper was extracted from the filtered water samples using standard nitric acid ( H N 0 ) and hydrochloric acid (HC1) digestion (20); recoveries from spiked samples were 96.9 ± 3.4%. Particulate-phase copper concentrations were determined by extracting particulates captured on filter papers with a diethylenetriaminepentaacetic acid (DTPA) solution (27); recoveries of copper from spiked samples were 102.0 ± 6.8%. A l l samples were analyzed using a Varian SpectrAA 300/400 atomic absorption spectrophotometer (wavelength: 324.8 nm, flame: air acetylene); minimum instrumental detection limit for copper was 0.03 ± 0 . 0 1 μg/mL(75 19). 3

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Statistical Analysis Analysis of variance ( A N O V A ) was performed comparing runoff collected during each of the field seasons. Least significant difference determined statistical significance between treatment means for each runoff event (22). The single criteria of classification for the data during the 1998 and 1999 field seasons were mulch treatment, POLY-Bare or V E T C H , while the single criteria for data classification in the 2000 and 2001 field seasons were

Mention of specific products or supplies is for identification and does not imply endorsement by U.S. Department of Agriculture to the exclusion of other suitable products or suppliers.


234 furrow treatment, POLY-Bare or POLY-Rye. Correlation analyses were performed to identify factors that had the greatest impact on dissolved- or particulate-phase copper loading.

Results and Discussion


Production A n important consideration for growers who want to adopt organic farming practices is the impact on harvest yields. Several researchers have reported previously on the positive economic feasibility and greater harvest yields of the V E T C H management practice relative to the conventional management practice of POLY-Bare (average tomato yield for 1991 to 1996: POLY-Bare = 6,820 ± 2,010 g/m , V E T C H = 8,690 ± 1,690 g/m ) (23, 24). In this study, no significant difference in harvest yield was observed between the POLY-Bare and P O L Y Rye management practices within each year (2000: POLY-Bare = 2,380 ± 630 g/m , POLY-Rye = 2,040 ± 600 g/m ; 2001: POLY-Bare = 3,850 ± 965 g/m , POLY-Rye = 4,010 ± 1,400 g/m ); however, 2001 was almost two times more productive as a function of cooler weather in 2000. 2

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Runoff Volume Runoff volume is influenced by the rate and quantity of rainfall and rainfall infiltration. The practice of covering raised tomato-beds with polyethylene mulch greatly reduces rainfall infiltration because 50 to 75% of the field is covered with an impermeable surface. McCall et al. (//) and Wan and E l Swaify (12) reported greater runoff volumes associated with the use of impermeable plastic mulch relative to bare soil.

POLY-Bare vs. VETCH In this study, significantly (p = 0.05) larger volumes of runoff were collected from POLY-Bare than from V E T C H plots in 94% and 92% of the events measured in 1998 and 1999, respectively. Plots with polyethylene mulch had up to thirty-four times more runoff than the vegetative mulch plots for individual storm events (8, 11). The seasonal water loss for the 1998 and 1999 growing seasons are presented in Figure 1A. The observed decrease in runoff


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Seasonal Runoff Volume


POLY-Bare POLY-Rye • VETCH

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Seasonal Soil Loss • POLY-Bare ^POLY-Rye • VETCH

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Figure 1. Seasonal runoff volume (A) and soil loss (B) from the polyethylene mulch/bare-soil furrow plots (POLY-Bare), polyethylene mulch/cereal rye furrows plots (POLY-Rye), and hairy vetch residue mulch plots (VETCH). Error bars represent the standard deviation of the mean.


236 volume (75% in 1998; 48% in 1999) for V E T C H plots relative to the P O L Y Bare plots is the result of the dissipation of rain drop energy and greater rainfall infiltration.


POLY-Bare vs. POLY-Rye As expected, significantly (p = 0.05) larger volumes of runoff were also collected from POLY-Bare than POLY-Rye for 80% of the runoff events in 2000 and 62% of the runoff events in 2001 (19). Runoff volumes from plots with bare-soil furrows were up to eight times greater than the runoff volumes from the plots with vegetative furrows for individual storm events. Seasonal water losses for the 2000 and 2001 growing seasons are presented in Figure 1A. The runoff volume from POLY-Rye plots was reduced by 41% in 2000 and 66% in 2001 relative to the plots with bare soil furrows (POLY-Bare). This reduction may be due to increased water demand and reduced soil moisture associated with living vegetation in the furrows, changes in soil structure, and the ability of rye residues to dissipate the energy of rain drops and effectively reduce the velocity of surface runoff allowing for greater infiltration within the furrows (25-28).

Soil Erosion 2

Soil loss (g/m ) was calculated based on the total volume of runoff water collected per plot per runoff event, the mass of filterable suspended-solids per volume of runoff, and the size of each plot.

POLY-Bare vs. VETCH The mean concentration (mg/L) of suspended-solids in runoff water from the POLY-Bare plots was four times greater than the concentrations measured in runoff from the V E T C H plots (geometric mean for 1997, 1998 and 1999 = 3,330 mg/L for POLY-Bare plots and 692 mg/L for V E T C H plots; range of individual runoff events for 1997, 1998, and 1999 = 424 to 16,810 mg/L for POLY-Bare plots and 12 to 6,952 mg/L for V E T C H plots). When runoff volumes were considered, significantly (p = 0.01) greater loads of soil were lost with runoff from polyethylene mulch plots. Although the average soil losses for individual runoff events were up to 24 times greater from the POLY-Bare plots than the V E T C H plots, the average soil losses for the 1998 and 1999 growing seasons were 6 and 4 times greater from polyethylene mulch than the vegetative residue mulch as shown in Figure IB (70, 75).


237 POLY-Bare vs. POLY-Rye Implementation of vegetative furrows in the polyethylene mulch production system significantly reduced the quantity of soil loading associated with runoff in 94% and 90% of the runoff events in 2000 and 2001, respectively. Runoff from POLY-Bare plots contained up to 24 times the concentration (g/mL) of suspended-solids than runoff from POLY-Rye plots with average particulate concentrations for POLY-Bare plots 4 and 5 times greater than from POLY-Rye plots (geometric means = 6,436 mg/L [2000] and 8,385 mg/L [2001] for P O L Y Bare plots and 1,694 mg/L [2000] and 1,704 mg/L [2001] for POLY-Rye plots; range of individual runoff events for 2000 and 2001 = 353 to 18,642 mg/L for POLY-Bare plots and 84 to 5,225 mg/L for V E T C H plots). The load of soil (g/m ) measured in individual runoff events from the POLY-Bare plots was 2 to 44 times greater than the amount measured in the runoff from the plots with vegetative furrows. The average soil loss for the 2000 and 2001 growing seasons is presented in Figure IB (19). The greater runoff volume and flow rates associated with the POLY-Bare plots increased the opportunity for off-site transport of soil with runoff. Planting cereal rye between raised polyethylene-covered vegetable beds reduced the velocity of runoff flow by 1.3 to 2.4 times that of the POLY-Bare plots. Replacement of the polyethylene mulch with hairy vetch residue mulch further reduced runoff volumes with flow rates that were 1.2 and 7.5 times less than the runoff from the POLY-Bare plots. The significant reduction in soil loading with the two alternative management practices, containing either vegetative furrows or vegetative furrows and beds, is the result of the anchoring characteristics of plant roots providing increased structural stability of the vegetated soil and the ability of crop residues to dissipate the energy of raindrops and effectively reduce the velocity of surface runoff (25-30).


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Copper Fate Copper is present in both soluble and particulate forms in the environment. The chemical form of copper is important to its bioavailability, behavior in biological processes, and its toxicity to aquatic organisms. In aerated water with a p H range of most natural waters (6 to 8), cuprous copper (Cu ) is unstable and will oxidize to the cupric form (Cu ), which is the predominant oxidation state in soluble aqueous complexes and considered the most environmentally relevant and toxic form to aquatic life (31-33). Cupric ions may sorb to organic particulates, sediments and clays, and form complexes with organic or inorganic compounds (34, 35). +1

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238 Dissolved-phase Copper Significantly (p = 0.01) greater loads of copper were measured in the dissolved-phase runoff from POLY-Bare plots (0.12-1.75 mg/m ) than V E T C H plots (0.06-0.84 mg/m ) in all runoff events following the application of copper hydroxide (Figure 2A). At the completion of the field season, dissolved-phase copper loads represented 1.39% and 0.39% of the copper applied to the P O L Y Bare plots and V E T C H plots, respectively. Correlation analysis (r) revealed that runoff volume contributed more to the increased copper load than the concentration of copper measured in the filtered runoff water (POLY-Bare: r = 0.66 volume, r = 0.46 copper concentration; V E T C H : r = 0.90 volume, r = 0.03 copper concentration). Dissolved-phase copper loads were greater in the runoff from POLY-Bare plots (0.04 to 7.0 mg/m ) than POLY-Rye plots (0.02 to 2.0 mg/m ) for half of the runoff events following the application of copper hydroxide (Figure 3A). The seasonal load of copper measured in the dissolved-phase of the runoff was 2.4 times greater in plots with bare-soil furrows than vegetative furrows, which represented 2.1% and 0.9% of the applied copper, respectively. Correlation analysis indicated that the greater dissolved-phase loads of copper from plots with bare-soil furrows were the result of the increased runoff volume rather than a difference in dissolved-phase copper concentrations (correlation analysis (r): POLY-Bare: r = 0.93 volume, r = 0.002 copper concentration; POLY-Rye: r = 0.84 volume, r = 0.03 copper concentration). 2


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Ρarticulate-phase Copper Individual runoff events collected from POLY-Bare plots contained significantly (p = 0.05) greater loads of particulate-phase copper than runoff from V E T C H plots (0.99-60.6 mg/m for polyethylene; 0.06-8.65 mg/m for hairy vetch) (Figure 2B). Copper loads in the particulate-phase of runoff represented 34.55% and 3.76% of the copper applied during the 1999 season for POLY-Bare plots and V E T C H plots, respectively. Correlation analysis (r) of the initial runoff event following the application of copper hydroxide revealed that particulate-phase loads of copper were attributed more to the quantity of soil lost with runoff than the concentration of copper associated with the particulates (POLY-Bare: r = 0.88 soil loss, r = 0.00 copper concentration; V E T C H : r = 0.75 soil loss, r = 0.19 copper concentration). Runoff collected from POLY-Bare plots (0.8 to 136 mg/m per runoff event) contained two to five times greater loads of particulate-phase copper than runoff from POLY-Rye plots (0.3 to 28 mg/m per runoff event) (Figure 3B). Seasonal copper loads measured in the particulate-phase of runoff were 32.6% (POLY-Bare) and 8.8% (POLY-Rye) of the copper applied during the 2001 2

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239 1999 Dissolved Phase • POLY-Bare • VETCH d) (11)


(8)

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Q. o 140 Ο 120

Particulate Phase τ

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Julian day Figure 2. Dissolved-phase (A) and particulate-phase (B) loads of copper in the runofffrom POLY-Bare and VETCH plots. Error bars represent the standard deviation of the mean. Numbers in parentheses represent days between copper hydroxide application and runoff.

growing season. Suspended-particles from the POLY-Rye plots contained greater concentrations of copper than particulates from POLY-Bare plots. However, correlation analysis (r) of runoff events following the application of copper hydroxide showed that particulate-phase loads of copper were attributed more to the quantity of soil lost with runoff than the concentration of copper on the particulates (POLY-Bare: r = 0.98 soil loss, r = 0.002 copper concentration; POLY-Rye = 0.99 soil loss, r = 0.06 copper concentration).


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2001 Dissolved Phase

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• POLY-Rye

(0.5)

(3)

(3)

(1)

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Julian day Figure 3. Dissolved-phase (A) and particulate-phase (B) loads of copper in the runoff from POLY-Bare and POLY-Rye plots. The difference in copper loads between the two management practices was significant (p=0.05) for runoff events on Julian day 229, 232, 235, and 242.


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Phase Distribution Although copper hydroxide is applied to the tomato plants, inevitably, a percentage of this fungicide is either washed off the foliage onto the mulch or directly applied to the mulch during foliar application. Copper is readily washed off polyethylene mulch and transported in surface runoff long after application (>30 days post application) (13). Furthermore, over 80% of the copper load was measured in the particulate-phase of the runoff for the three management practices (POLY-Bare = 86.7 ± 14.3%, 93 ± 6.5%; POLY-Rye = 88 ± 11%; V E T C H = 81.7 ± 13.0%) (Figure 2A & 2B, Figure 3A & 3B). The impervious nature of polyethylene mulch produces greater volumes of runoff with larger sediment loads (70-/2), resulting in greater off-site transport of copper from the area of application. Thus, controlling soil losses in runoff is critical to decreasing total copper released from the field.

Ecotoxicological Concerns Runoff from tomato production with polyethylene mulch has been implicated in the failure of commercial shellfish farms in the Mid-Atlantic Region of the United States. When freshwater containing copper-sorbed particulates comes in contact with seawater in estuarine environments copper is desorbed from the particulates as soluble copper (36, 37), which is more bioavailable to aquatic organisms. Aquatic biota may bioconcentrate copper in their tissue (bioconcentration factors: 28,200 for saltwater bivalves, 2,000 for freshwater algae) (32) and copper is acutely toxic to aquatic species at low levels (1.3 μg/L for Daphnia tested in freshwater, 1.2 μg/L for a bivalve tested in saltwater) (14-18). Copper has been shown to adversely affect fish, causing histological alterations in chemoreceptors, mechanoreceptors, and gill, kidney, and hematopoietic tissues (17, 18), and result in reproductive effects such as reduced egg production and abnormalities in newly hatched fry (18). Dietrich et al. (37) reported that copper levels in a tidal creek receiving runoff from an agricultural area utilizing polyethylene mulch (POLY-Bare), were as high as 22 μg/L, which exceeds the measured median lethal concentration ( L C ) for larval clams (Mercenaria mercenaria) at 96 h ( L C = 21 μg/L) and 192 h ( L C = 12 μg/L). Based on the results of our field investigations, implementation of alternative management practices that either maintain the polyethylene mulch but replace bare soil furrows with vegetative furrows (POLY-Rye) or completely replace the impermeable polyethylene mulch with vegetative residue mulch (VETCH) will reduce copper loads with runoff by an average of 72% and 88 %, respectively. Therefore, surface water concentrations could be reduced from 22 μg/L to approximately 6 and 3 μg/L, which are below the L C for larval clams, assuming agricultural runoff was the primary source of copper. These reduced concentrations are also near or below the E P A guidelines 50

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5 0


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Copper Concentration in Creek Water

Figure 4. Impact of agricultural management practices on the concentration of copper in a creek receiving runofffromfresh-marketvegetable production, fw =freshwater, sw = saltwater.

(31) to protect freshwater and saltwater aquatic life (24-h average = 5.4 μg IL for fresh water and 4.0 μg IL for salt water) (Figure 4).

Conclusion The results of this study have clearly demonstrated that management practices can have a profound impact on agrochemical fate, even i f both the cultivation method and the chemical are allowed under N O P standards. The chemical characteristics and toxicity of copper-based products require that they be used in a judicious and environmentally-friendly manner to avoid negative impacts on surrounding ecosystems.

References 1. 2.

U S D A Alternative Farming Systems Information Center, Organic Food Production; U R L http://www.nal.usda.gov/afsic/ofp/ofp.htm U S D A Economic Research Service, Organic Production 1992-2003; U R L http://www.ers.usda.gOv/Data/Organic/#tables. November 2005.


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244 22. Steel, R. G . D.; Torrie, J. H . Principles and Procedures of Statistics: A Biometrical Approach; McGraw-Hill Book Company: New York, N Y , 1980. 23. Kelly, T.; L u , Y.; Abdul-Baki, Α.; Teasdale, J. J. Am. Soc. Hort. Sci. 1995, 120, 854-860. 24. Abdul-Baki, Α.; Teasdale, J.; Korcak, R.; Chitwood, D.; Huettel, R. Hort. Sci. 1996, 31, 65-69. 25. Mannering, J.; Meyer, L . Soil. Sci. Soc. Amer. Proc. 1963, 27, 84-86. 26. Gulick, S.; Grimes, D.; Munk, D.; Goldhamer, D. Soil Sci. Soc. Amer. J. 1994, 58, 1539-1546. 27. Sollins, P.; Radulovich, R. Soil Sci. Soc. Amer. J. 1988, 52, 1168-1173. 28. Foster, G . L . ; Meyer, L . D . Erosion mechanics of mulches; American Society of Agricultural Engineers: St. Joseph, MI, 1972; Paper no. 72-754. 29. Sur, H . ; Mastana, P.; Hadda, M. Trop. Agric. (Trinidad) 1992, 69, 319-322 30. Zuzel, J.; Pikul, J. Soil Sci. 1993, 156, 111-117. 31. U.S. Environmental Protection Agency. Ambient Water Quality Criteria for Copper; E P A 440/5-80-036: Washington, D C , 1980. 32. U.S. Environmental Protection Agency. Ambient Aquatic Life Criteria for Copper; E P A 440/5-84-031: Washington, D C , 1985. 33. Garrels, R. M.; Christ, C. L. Solutions, Minerals and Equilibria; Harper and Row: New York, N Y , 1965. 34. Riemer, D.; Toth, S. J. Am. Water Works Assoc. 1969, 62, 195-201. 35. Stiff, M. Water Res. 1971, 5, 585-596. 36. Thomas, D.; Grill, E . Estuarine Coastal Mar. Sci. 1977, 5, 421-435. 37. Dietrich, Α.; Gallagher, D . J. Agric. Food Chem. 2002, 50, 4409-4416.


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